Our previously reported methods for purification of complement components continue to be improved and updated according to our laboratory requirements and the properties of the isolated components (i.e., stability, concentration in plasma, and ease of isolation). Large scale isolation of C3, C4, C5, C9 and factor H has been well established and procedures for improved resolution of P, I, C2, B, C7, C8 and C6 early in their isolation have been developed, although the overall recovery of these latter components during isolation needs to be improved. We have adapted an affinity technique using C4b-Sepharose for the rapid, final purification with full recovery of human C2 from serum. C2 obtained this way is pure as judged by SDS-PAGE, alkaline PAGE and does not contain factor B, C7 or C4 by the immunoblotting technique. The only detectable contamination is a low level of IgA. Spontaneous loss of C3 activity associated with its isolation and storage requires more frequent purification of this labile component. The new isolation procedure we report was specifically designed to rapidly isolate C3 from smaller volumes of EDTA-plasma (60 ml) in three short steps. Pure C3 with full specific hemolytic activity can be prepared in three days with this protocol. Monospecific antibody to C1-In has been raised in a goat to this protein purified by our recently developed isolation scheme. The antibody to C1-In is being used to isolate a non-functional variant of C1-In from the plasma of a patient with an acquired form of hereditary angioedema. Methods to prepare C5a from citrated plasma have been finalized and the C5a obtained has been physico-chemically and biologically characterized. Final purification of C6 and C4 is in progress.